1. Field of the Invention
The invention relates to an internal combustion engine shutdown device, and in particular to a device for a sequential controlled stopping of such an engine used to power a center pivot irrigation pump.
2. Discussion of the Technical Problems
Internal combustion engines including diesel and gasoline fueled engines are often used as a source of stationary power in applications where the operation of the engine is controlled by automatic devices instead of by human operators. One such application is in a center pivot irrigation system in which the engine is used to provide power to run the pump.
As conditions change which effect the continued safe operation of such a system, the engine must be stopped until the condition is remedied. A missalignment in a center pivot is one example of a condition which would necessitate an engine shutdown. Since the operator is not available to stop the engine, the shutdown must be accomplished automatically.
The ordinary device for automatically stopping an engine used to provide power to a pump in a center pivot irrigation system is a conventional "kill switch" which is is a switch directly sensitive to misalignment or some other unsafe condition. When the kill switch is activated by the unsafe condition, it shuts off the engine by shutting off the ignition or stopping the fuel from reaching the engine. The use of such a directly connected kill switch to stop an engine is well known in the art.
A kill switch can also be used in an indirect method of stopping an engine. One example of an indirect method is the use of a normally energized kill switch (energized while operating) which is de-energized in the event that pump pressure falls below a certain set point. Such an irrigation system is also fitted with a mechanical dump valve which opens in the event of a misalignment, thereby decreasing pump pressure and de-energizing the kill switch. As in the direct system, once the kill switch is de-energized the engine is immediately stopped.
Many stationary installations of internal combustion engines set the operating speed of the engine at a very high rate in order to achieve the best efficiency and power level. While operating within these high power settings the engines develop high internal temperatures. Unfortunately, the stopping of an engine abruptly at such a high power setting can damage the engine and reduce engine life. On the other hand, a reduction to idle speed followed by a time period for the engine to stabilize at the lower power setting would tend to prolong engine life and minimize engine wear.
In many applications, such as in a center pivot irrigation system, the system is protected from losing the water prime by having a check valve installed in the irrigation supply line. If the engine is abruptly brought to a stop, the sudden pressure surge against the check valve could cause damage to the valve or to the pump itself. By reducing engine speed to idle for a period of time, the pressure is reduced in stages without a potentially damaging surge.
Prior art "kill switch" engine stopping devices do not allow the engine speed to be reduced for a period of time to avoid excessive wear to the engine or other damage to the pump and/or the supply line. The engine is abruptly stopped by cutting off the fuel to the engine or by switching off the ignition system by the kill switch. Diesel and gasoline engines are normally stopped by closing off the fuel supply while natural gas and propane fueled engines are normally stopped by cutting off the ignition.
Examples of a number of prior art engine shut-down devices can be found in representative patents. Generally, the prior art relates to devices adapted to engines used in motor vehicles which must be shutoff due to a collision or some other emergency situation particular to motor vehicles. Very few devices relate to stationary engine applications and none known are directed to providing a controlled timed shutdown in order to reduce engine wear or system damage in the event of a problem in an external apparatus being powered by the engine.
U.S. Pat. No. 3,550,717 to Doty discloses a device that closes the fuel line in a moving engine in the event of a collision or theft. The invention brings about an immediate stopping of the engine rather than a reduction to idle speed first.
U.S. Pat. No. 3,371,667 to MacMillan disclosed a fail safe throttle control system for a vehicle in which the engine speed is reduced to idle in the event the accelerator is jammed. The invention provides for continued operation of the engine at a reduced speed rather than a timed shutdown.
U.S. Pat. No. 3,888,219 to Rogerson discloses an overspeed protection device for limiting the speed of a motor vehicle engine. The invention relates to the throttle linkage and is not responsive to an external condition.
U.S. Pat. No. 4,102,316 to Valbert relates to a hydromechanical shutoff for an internal combustion engine. The invention is actuated in response to internal conditions of the engine such as low oil pressure or high temperature and is not responsive to external conditions.
U.S. Pat. No. 4,106,469 to Dey discloses an automatic motor kill system in the event the air cleaning system becomes clogged. The invention is responsive to the internal condition of reduced manifold pressure.
U.S. Pat. No. 4,193,385 to Katsumata et al. discloses an engine stopping device for magneto ignition engines which such as lawnmowers which insures that the engine does not restart while it is in the process of stopping. The invention provides a device for stopping the engine by means of the ignition rather than by only shutting off the fuel.
U.S. Pat. No. 4,237,997 to Swanson discloses a switch and throttle lever combination to limit an overspeed condition in a snowmobile engine. The invention is not responsive to external conditions.
U.S. Pat. No. 4,333,827 to Cummins, II discloses an automatic shutdown device that is responsive to a reduced pressure of a pump inlet. The invention provides for an immediate engine stopping to prevent damage to the pump. Since the situation is an emergency, the engine must be stopped immediately. The device, while stopping the engine in response to reduced pressure does not provide for a time for the engine to operate at idle before the complete engine shutoff occurs.
As can be seen from the foregoing discussion, an inexpensive device is needed that will provide an automatic controlled shut down for a stationary engine in order to allow the engine operating parameters as well as pump system pressure to stabilize at a reduced level for an adjustable period of time before the engine is stopped. The device must be responsive to external conditions of both the direct and indirect type. It must be reliable and capable of being easily tested. The device should provide an adjustable idle operation time which can be set for the particular engine and equipment being powered by it. The device should be uncomplicated in design, easily installed on existing engines of numerous types, easily repaired, not subject to damage by vibration, and simple to manufacture. The instant invention is directed to all of these needs as well as to others as explained in the following summary.